1. Field of the Invention
The present invention relates to a method for manufacturing a closed impeller that has a simple configuration and enables fusion in a very accurate position.
2. Description of the Related Art
Environmental concerns and cost efficiency issues created increased expectations and demand for vehicles with reduced fuel consumption. A variety of means have been used to reduce fuel consumption, and increase in efficiency is one of them. Water pumps are provided on vehicles (vehicles equipped with a gasoline engine, hybrid vehicles, and electric automobiles) to cool the engine and warm up the cabin. Due to a recently created demand for reduced power consumption and therefore for increased efficiency, water pumps have also been the object of active development aimed at additional increase in efficiency.
There are impellers for water pumps that are provided with the so-called front plate. Examples of such impellers provided with the front plate are described in Japanese Patent Application Laid-Open No. 53-54301 and U.S. Pat. No. 5,538,395. A structure in which a base plate (disk) serving as a base is provided in the root portion of the impeller blade has been widely implemented as a typical structure of a resin impeller, but an impeller structure in which a hole is provided in the central portion on the distal end (intake) side of the impeller blade and a front plate is provided to cover the impeller blade circumferentially has also been widely used to attain the increased efficiency.
In most manufacturing methods, the front plate, impeller blade, and base plate that are originally separate components are integrated in the production process and the front plate is eventually integrated with the impeller blade. This method is widely used for resin impellers because the components can be easily fused. Against the background of using the resin impellers, the increase in efficiency that is attained because the impeller blade shape can be set easier than in the case of conventional pressed (sheet metal) impellers and the reduction in weight with respect to the pressed (sheet metal) impellers also serve as important factor. The impeller in which the front plate is thus integrated with the impeller blade (having the base plate attached thereto) is called “closed impeller”.
Japanese Patent Application Laid-Open No. 53-54301 discloses a manufacturing method of fusing “a member in which a front plate (front surface shroud 1) is integrated with an impeller blade (impeller blade portion 2)” and “a base plate (back surface shroud 3)” and a structure obtained thereby. U.S. Pat. No. 5,538,395 discloses a structure in which “a front plate (cover 2)” and “a member (bottom 1) in which an impeller blade and a base plate are integrated” are fused together and a manufacturing method therefor. A large number of means can be used for fusing two or more resin parts together, those parts being not limited to resin impellers. Examples of suitable means include: (1) ultrasonic waves, (2) vibrations, (3) laser, (4) heat plate, and (5) high-frequency radiation.
(1) Ultrasonic waves: resins are melted and fused together by applying sound waves with a frequency of about several tens of thousands of hertz to the components to be fused.
Typically, when the surfaces (flat surfaces) to be fused are pressed against each other in the vertical direction, the resin is not melted at the surfaces even when ultrasonic waves are applied. For this reason, one surface is left flat, but protrusions of a triangular shape are provided at the other surface to be fused as described in Japanese Patent Application Laid-Open No. 53-54301: FIG. 2 (see FIGS. 9A and 9B of the present application), FIG. 4 (see FIG. 9C of the present application), FIG. 5 (see FIGS. 9D and 9E of the present application), FIG. 6 and FIG. 7; U.S. Pat. No. 5,538,395: FIG. 2A, FIG. 3A, FIG. 4A, FIG. 4B (see FIG. 8B of the present application), FIG. 4C (see FIG. 8A of the present application), FIG. 5. Here ultrasonic waves are applied after the flat surface and surface with triangular protrusions have been pressed against each other, the resin starts melting at the tips of the triangular protrusions, and the two surfaces are fused together.
(2) Vibrations: a method by which the resin is melted by applying vibrations of a frequency of about several hundreds of hertz and fused.
(3) Laser: a method by which a laser beam is directed towards the zones to be fused and the resin is melted and fused.
(4) Hot plate: a method by which the resins at both sides are preheated to a high temperature and then pressed against each other to melt and fuse the resin surfaces.
(5) High frequency: a method by which a needle-shaped metal is heated by applying high frequency thereto and a resin surrounding the metal heated by the application of high frequency is melted and fused. Other fusion methods also exist, but the important fusion methods are described above.
In all these fusion methods, natural cooling is conducted once the resin of the surfaces to be fused has melted, the melted resin solidifies, and the surfaces are fixedly attached to each other.
The case in which “the member in which the front plate is integrated with the impeller blade” and the “base plate” are fused together, as in Japanese Patent Application Laid-Open No. 53-54301, will be investigated below in greater detail. When such fusion of components is conducted, the surfaces to be fused are both flat, as shown in the drawings of Japanese Patent Application Laid-Open No. 53-54301. Further, the description indicates that the flat surfaces are pressed against each other and ultrasonic fusion is conducted. Such fusion has the following features and limitations.
Because flat surfaces of two members are pressed against each other and irradiated by ultrasonic waves, very small vibrations are generated in the two members irradiated with ultrasonic waves. Because the two members are made from a resin and the resin does not withstand a large force if the members are pressed against each other too strongly, the members cannot be pressed together by a large force. Therefore, the aforementioned small vibrations cause relative displacement of the two members. In this case, because the surfaces to be fused are flat, as described in Japanese Patent Application Laid-Open No. 53-54301, the impeller itself does not provide any means for inhibiting the displacement, and the two members move independently in the respective directions. The resultant significant drawback is that the back surface shroud 3 and impeller blade portion 2 easily shift relative to each other in the radial (transverse) direction. Accordingly, in order to prevent such a radial (transverse) displacement, the fusion has to be conducted by providing a ring-shaped positioning member on the outside of the impeller in the circumferential direction with a certain gap between the impeller and the positioning member.
From another standpoint, because flat surfaces are fused together as shown in FIG. 2 of Japanese Patent Application Laid-Open No. 53-54301, even when the front surface shroud 1 and impeller blade portion 2 are fused together supposedly as separate component, because the front surface shroud 1 has a flat surface and the side end surface of the impeller blade portion 2 is also flat, it is still necessary to conduct fusion by providing the positioning member in the same manner as described above. Thus, where the front surface shroud 1 and the side end surface of the impeller blade portion 2 are to be fused together without using the positioning member, a displacement in the radial (transverse) direction can occur between the front surface shroud 1 and impeller blade portion 2. Because of such displacement in the radial (transverse) direction, an eccentric centrifugal force acts upon the front surface shroud 1 when the impeller is rotated and the service life of the bearing subjected to such eccentric centrifugal force can be shortened. In addition, because the front surface shroud 1 is disposed with a displacement in the radial (transverse) direction, a region where the front surface shroud 1 is not present that corresponds in size to the displacement amount of the front surface shroud 1 appears on the opposite side in the displacement direction of the front surface shroud 1. Since there appears a region having no front surface shroud 1 that is provided to increase the discharge performance, the pump capacity can be reduced.
Observing the impeller blade tip surface 14 described in U.S. Pat. No. 5,538,395, FIG. 4C (see FIG. 8A of the present application), FIG. 4B (see FIG. 8B of the present application), and other drawings, protrusions of triangular shape for fusion are provided over the entire region of the impeller blade tip surface, as shown in the drawings. In other words, the entire surface of the impeller blade tip surface is a protrusion of a triangular shape for fusion. Conversely, no surface similar in shape to the so-called flat surface is present at the impeller blade tip surface. The impeller blade tip surface can be fused to the front plate by forming the protrusion of a triangular shape for fusion over the entire surface of the impeller blade tip surface, assembling with the front plate, and applying a fusion means such as ultrasonic waves, vibrations, laser, heat plate, and high frequency. High frequency is used in the examples of U.S. Pat. No. 5,538,395.
With the above-described fusion method, fusion can be attained, but although the fusion is possible, the following problems are encountered at the stage of actual implementation. Thus, there is a time interval (period) in which ultrasonic waves, vibrations, or high frequency are applied to the surfaces to be fused, as described in U.S. Pat. No. 5,538,395, in a state in which the resin of the surfaces to be fused is in a molten state produced by the fusion means. Fine observation of the molten state of the resin at the surfaces to be fused demonstrates that the molten resin is present at the impelled blade tip surface and the front plate assumes a floating state thereabove with the molten resin being interposed therebetween. Where the ultrasonic waves, vibrations, or high frequency are applied in such a floating state of the front plate, the front plate can be easily shifted in the radial (transverse) direction.
In order to prevent such “a displacement of the front plate during fusion”, a positioning member of a circular shape that has a diameter slightly larger than that of the front plate is disposed in the same manner as described in Japanese Patent Application Laid-Open No. 53-54301 on the outer circumference of the front plate so as to prevent the front plate from shifting in the radial (transverse) direction. One means for reducing the displacement of the front plate and impeller in the radial (transverse) direction during fusion involves reducing the clearance between the front plate and the positioning member, but where the clearance is simply reduced, it becomes difficult to insert the front plate into the positioning member when the two are assembled. The resultant problem is that productivity drops.
Further, when fusion is conducted without using the positioning member, the front plate is fixedly attached in a state in which the center of gravity thereof is shifted outward from the impeller center. Therefore, when the water pump operates, an eccentric centrifugal force act upon the front plate and the service life of the bearing subjected to such eccentric centrifugal force can be shortened. In addition, because the front plate is disposed with a displacement in the radial (transverse) direction, a region where the front plate is not present that corresponds in size to the displacement amount of the front plate appears on the opposite side in the displacement direction of the front plate. Since there appears a region having no front plate that is provided to increase the discharge performance, the pump capacity can be reduced.
Further, in the configuration described in U.S. Pat. No. 5,538,395, as shown in FIG. 8D, where the height of the impeller blade tip surface 14 is denoted by W0 and the height of the triangular protrusion is denoted by W1, when the impeller blade tip surface and the front plate are fused by applying a fusion means such as high frequency, depending on the fusion degree of the triangular protrusions, the height of the base plate and the lower surface of the front plate becomes the height W that normally does not have a constant value, as shown in FIG. 8D.